Electric heating device.



T. VAN ALLER.

ELECTRIC HEATING DEVICE.

APPLICATION FILED JUNE 7, 1912.

Figl.

TYEHU 172m! LLEH Patented June 30, 1914.

JNVENTUR I .565 ATTUHNEY.

UNITED STATES PATENT OFFICE.

TYCHO VAN ALLER, OF SCHENECTADY, NEW YORK, ASSIGNOR T0 GENERAL ELECTRICCOMPANY, A CORPORATION OF NEW YORK.

ELECTRIC HEATING DEVICE.

Specification of Letters Patent.

PatentedJune 30, 1914.

Application filed June 7, 1912. Serial No. 702,158.

To all whom it may concern:

Be it known that I, TYCHOVAN ALL-ER, a citizen of the United States,residing at Schenectady, in the .county of Schenectady, State of NewYork, have invented certain new and useful Improvements in ElectricHeating Devices, of which the following is a specification.

This invention relates to electric heating devices, one of the objectsof my invention being to provide means whereby a device of thischaracter may be automaticall controlled in a reliable, simple and ecient manner,

In the use of such electric heating devices as fiat-irons and the like,it is desirable that the heat generated should be varied to aconsiderable extent. In the case of a fiatiron, for instance, the amountof heat required will depend upon the nature of the work done. heavy,damp material, a relatively large amount of heat must be generated,otherwise j the iron will become too cool to operate effectively. On theother hand, if the iron is being used on thin material which isrelatively dry, a small amount of heat should? be furnished, in orderthat the iron shall not become overheated. In other words, it. isdesirable that the supply of heat be automatically regulated to thedemand.

One of the objects of my invention is to J provide an electricallyheated device of the character in which the demand for heatis variable,with a heating unit which of itself f will regulate the amount ofcurrent supplied at any particular time to the demand at that I ancewire may be operated at a high tem- Another object ofmy invention is topro- 5 vide improved means whereby, in case the heat supplied is notbeing used, the current will be cut off so as to save current and intime.

some cases to prevent serious scorching or perhaps fire, as for instancewhere the iron is accidentally left in contact with the work for aconsiderable time.

material having a positive temperature coefficient, 11.6., one in whichthe specific resistance will increase with the temperature and rely uponthe heating element for the reeistance variation. It has been heretoforeproposed .to use a resistance element of this character, but since therange of variation If the iron is being used on of resistance with thearrangement sug-- gestcd was small, a resistance material having apositive temperature coeflicient was merely employed as ,an auxiliary orseparate resistance for reducing the current, the change in the specificresistance being taken advantage of to cause a relay to operate and varythe amount of extra resistance in circuit. I have found that certainmetals, such, for instance, as iron, having a positive temperaturecoefficient, may be employed in such a way that the resistance clementitself will furnish sufficient variation of resistance upon change oftemperature to regulate the supply of current to the demand within thelimits of practical requirements. Iihave found, for instance, that byusing iron as the resistance element and causing it to operateefficiently throughout a wide range of temperature that practicallyperfect regulation can be obtained. To this end, I preferably, thoughnot always necessarily, provide some means for preventing oxidation ofthe 11011 or other resistance metal, and

therefore make it possible to operate the perature, at which it wouldotherwise quickly oxidize, without any noticeable oxidation, so that awide range of temperature and therefore a wide range of current valuesmay be employed.

In carrying out the second object of my invention, I provide meanswhereby, in case the specific resistance of the resistance .element isincreased to a predetermined extent by the increase in temperature, thedecrease of current flow incident thereto will cause the circuit to beopened' and the fiat-iron or similar device permanently cut out ofcircuit. Assuming the case of a fiat-iron accidentally left by theoperator in contact with .a piece of cotton material, the heat not beingcarried away by contact with damp or which would cause the material tobe scorched, I cause the circuit to be opened and cut out the fiat-ironentirely. This is I preferably accomplished by the opening of anunder-load cutout switch which can only be closed by hand after thetemperature has dropped to a safe value.

Other objects and purposes of my invention will appear in the course ofthe following specification, in which I have shown my invention embodiedin concrete form for purposes of illustration.

In the accompanying drawings illustrating my invention embodied inconcrete form,

Figure 1 is a plan view of a flat-iron with the upper plate removed toshow the heating unit; and Fig. 2 is a similar view showing theflat-iron provided with an automatic cutout.

Referring to the drawing, 1 represents the base of a flat-iron having aresistance element 2 mounted in heat conductive relation therewith. Forpurposes of illustration, I have shown the unit as consisting of a metalribbon 2 wound upon a flat V-shaped support of insulating material 3,such as mica or the like, although any suitable arrangement orconstruction of the unit may be employed without departing from thespirit of my invention. The material of the ribbon 2 is preferably ofiron or other metal having a high positive temperature coefiicient ofresistance. The unit is placed in good thermal relation with the ironbase so that any change in temperature of the base will be quicklycommunicated to the heating unit and the heat from the unit will bequickly communicated to the iron. This good thermal relationship betweenthe unit and the iron is exceedingly important. The metal of theresistance ribbon having a positive temperature coefficient will causethe current supplied to the iron base and hence the heat suppliedthereto to automatically regulate itself to the demand. If, for instancethe iron base is placed in contact with heavy damp material, the ironbase will, of course, be quickly cooled. Owing to the good thermalrelationship between the iron and the unit, this decrease of temperaturewill cause heat to be quickly extracted from the heating unit and thetemperature of the heating unit to drop. This decrease of temperaturecauses the specific resistance of the resistance metal to be decreasedand consequentl a proportional increase in current flow. ince morecurrent will now flow through the resistance material, the temperatureof the unit will be increased and this increase in temperature will beimmediately communicated to the iron base. The net result is, that whilethe iron base will be cooled for an instant, an additional supply ofheat will immediately become available and the iron will promptly riseto the proper temperature. In this way, the temperature of the flat-ironmay be kept substantially uniform and the amount of current used variedwith the requirements. In other words, when work is being donewhichrequires only a small amount of heat, then only a small amount of heatis generated and a small amount of current consumed,

whereas when the work requires more heat order to accomplish this, it isnecessary thatv the metal shall in some cases attain a comparativelyhigh temperature. If, for instance, iron is used, this high, temperaturewill cause deterioration of the iron due to oxidation. In order toovercome this difficulty, I treat the metal in such a way as to renderit non-oxidizing even at a high temperature. This may be done veryeffectively, especially in the case of iron resistance material, bytreating the iron by the process described in my application abovereferred to. One method of carrying out this process, which has beenfound to be very successful in practice, is as follows: Powderedaluminum is thoroughly mixed with a certain percentage of powdered'zincand sal ammoniac and the metal to be treated is placed in an ovensurrounded by the powdered mixture. The oven is then completely closedand slowly rotated. A temperature of about 700 C. is maintained in theoven for about two hours. One mixture which has been found to giveexcellent results contained 60 pen cent. aluminum; 10 per cent. salammoniac; and 30 per cent. graphite. Iron wire treated by this processhas been ke t at red heat for over two hundred hours wit out anyapparent oxidation. It is obvious that by using iron wire treated inthis way a high temperature can be maintained for a long time withoutdeterioration of the unit, and thus the current supplied may be variedthroughout a wide range.

In Fig. 2, I have shown my device in connection with an automatic switchwhich will cut off the flat-iron when the current decreases to apredetermined value. Any well known form of underload cutout which issuitably calibrated and adjusted will serve my purpose. As shown in thedrawing, the cutoutsimply consists of a coil 4 which is adapted to beconnected in series with the heating wire :2 and with the supply lines 5and 6. A core 7 operating within the solenoid is weighted at its lowerend and connects through a rod 8 extending through a stationaryinsulating support 9 with an insulating member 10 having a flange ateach end. The switch member 11, in the form of a loop, is pivoted at 12so that its free end engages the spring contact 13 which is providedwith a shoulder 14 which latches the switch member in closed position.The flanges on the member 10 engage the switch member to open and closethe same. \Vhen the current is above a predetermined value, the corewill be held in raised position and the switch closed after it has oncebeen closed by means of the knob 15. In this raised position the circuitwill be closed through the winding 4, switch arm 11, and the resistancewire 2 of the flat-iron. hen the current in the winding 4 falls below apredetermined value, which value may be regulated by regulating theweights 16 upon the core, or in any other well known manner, the switchcontacts will be opened by the dropping of the core and the supply ofcurrent cut oif from the wire 2. This automatic cutout acts as a safetydevice to cut off the current in case the iron is left in circuit,either accidentally or otherwise, for so long a period and under suchconditions as might. cause fire. If. for instance, the flatiron shouldhe accidentally left in contact with inflammable material, thetemperature of the unit will rise and the resistance of the unitcorrespondingly increase. No means being supplied for carrying away theheat. the temperature will continue to rise and the current to decreaseuntil a balance is reached in which the radiation losses will equal theenergy input. The underload sw tch is therefore set so as to open thecircuit when the current is reduced to a predetermined valuecorresponding to a rise in temperature of the flat-iron beyond which itwould not be considered safe. If the fiatiron were left upon a stand,the radiating surface would be increased to such an extent that thetemperature might not rise to a point at which the cutout will operate,al though it can be set to operate at substantially any value. It willbe seen that I have provided an electrically heated device in which thecurrent supplied 18 automatically regulated to the demand solely bymeans of the heating unit itself and likewise provide automatic meansfor cutting off the heater if it becomes hot enough to be dangerous, andwhile I have described my invent-ion as embodied in concrete form and asoperatin in a specific mannerfor purposes of illustration, it should beunderstood that I do not limit myself thereto, since variousmodifications thereof will suggest themselves to those skilled in theart without departing from the spirit of my invention, the scope ofwhich is set. forth in the annexed claims.

What I claim as new, and desire to secure by Letters Patent ofthe UnitedStates, is I 1. An electric heating device comprising a. body to beheated and aresistance conductor composed of iron with a non-onidizablesurface and in good thermal relation w th said body so as to regulatethe heat supplied to said body by the changes of resistance of the ironconductor due to changes of temperature.

2. An electric heating device comprising a body to be heated, aresistance conductor for heating the same having a high positivetemperature coeflicient and arranged to regulate the heat delivered tothe said body by changes of resistance of said conductor due to changesof temperature, and an electroresponsive device for cutting the deviceout of circuit when the current in said conductor decreases to apredetermined value.

3. An electric heating device com rising a body to be heated, anon-oxidizab e resistance conductor for heating the same having a highpositive temperature coefiicient and 'arranged to regulate the heatdelivered to the said body by changes of resistance of said conductordue to changes of temperature, and an electromagnetic switch having itswinding in series with said conductor for cutting the conductor out ofcircuit when the current therein decreases to a predetermined value.

In witness whereof, I have hereunto set my hand this 6th day of June,1912.

TYCHO VAN ALLER. \Vitnesses BENJAMIN B. HULL, HELEN ORFORD.

